Some time ago someone claimed there was an ancient (ice age) river that flowed from the mountains of Saudi Arabia towards the tigris/Euphrates. His date for it drying up was close to the start of the predynastic so I wonder about people displace by the drying migrating to the nile (& later to mesapotamia). If they did it could explain similarities tween the 2 early civilizations - a wild speculation.

In 1922, Eduard Glaser proposed that the Garden of Eden was located in Eastern Arabia within the Dilmun civilization.[28] Scholar Juris Zarins also believes that the Garden of Eden was situated in Dilmun at the head of the Persian Gulf, where the Tigris and Euphrates Rivers run into the sea, from his research on this area using information from many different sources, including Landsat images from space. In this theory, the Bible’s Gihon would correspond with the Karun in Iran, and the Pishon River would correspond to the Wadi Batin river system that once drained the now dry, but once quite fertile central part of the Arabian Peninsula.[29] ...